(1) Field of the Invention
The present invention relates to sheet feeding devices in general, and in particular, devices which align and gate sheets into a work station.
(2) Prior Art
The use of sheet feeding devices for feeding sheets into timed relationship or synchronization with a relatively moving processing station is well known in the prior art. Such devices consist of a paper path extending from a sheet supply bin into the processing station. A sheet transport device is disposed within the paper path. A lateral edge aligner and a gate mechanism are usually disposed at appropriate zones of the paper path. The edge aligner is usually a flat surface against which the sheet is referenced to achieve lateral alignment. Gating and forward alignment (that is alignment in the direction of sheet motion) are achieved by registering the sheet against the gate mechanism. The gate mechanism generally runs transversely to the direction of sheet travel.
Although the above devices work well for their intended purpose, they are affected by several undesirable features. Usually, these devices require relatively long paper paths in order to perform the lateral and forward sheet alignment. The long paper path tends to increase the overall size and cost of the machine. Also scuffing the sheets against the alignment edge and gate mechanism results in damage to the sheet and creates paper dust.
U.S. Pat. No. 3,065,835 describes a high speed printing device and a drive mechanism for positioning a sheet relative to the printing device. The drive mechanism consists of eight drive nips disposed in orthogonal arrangements along the paper path of said device. Each drive nip is formed by a drive roller and a back-up roller. Four of the drive nips are utilized to position the sheet bidirectionally along the X axis. Likewise, the other four drive nips position the sheet bidirectionally along the Y axis. Each sheet has a preprinted grid pattern on one side. Sensors which are placed in the paper path sense the grid pattern and adjust the motor/brake assembly associated with the nips so that the sheet is advanced to successive printing positions.
U.S. Pat. No. 3,754,826 describes a drive mechanism which automatically corrects the orientation of a document so that the document is positioned in proper orientation to the document glass of a copier. The drive mechanism consists of a vacuum transport belt and a pair of switches disposed on a line normal to the direction of sheet travel. When the sheet is properly oriented, both sensors are activated simultaneously. When the sheet is not properly oriented, one of the sensors is picked before the other. The time lag between the actuation of the switches indicates skew and activates a system which adjusts the orientation of the belt to compensate for skew in the sheet.
U.S. Pat. Nos. 3,743,277 and 4,089,517 describe prior art devices which utilize sensors to sense the lateral position of a sheet and activate a positioning device to correct lateral offset.
Although the latter-cited prior art devices are an improvement over the previously mentioned devices which utilize gating and side registration members, the latter devices tend to be complex and do not perform all the necessary functions needed to align and gate a sheet into a work station.